US Defense Secretary James Mattis sees his ongoing visit to South Korea as a "listening trip" aimed at having a chance to learn what its allies think and say on key issues of mutual concerns, a diplomatic source said Friday.

Mattis, a retired Marine Corps general, arrived in South Korea on Thursday for a two-day stay. This is his first overseas trip since taking office, and he plans to leave for Japan after completing his itinerary here.

"We heard that he told his aides and Korean counterparts that his visit to Korea this time is a listening trip. He came here not to talk but to listen," the source close to the matter told Yonhap News Agency on condition of anonymity.

"We were also asked by his side to minimize press events or media exposure, while he is here in accordance with the nature of the visit, which is to listen to what allies have to say," he added.

Upon his arrival in Seoul on Thursday, Mattis held meetings with South Korea's Acting President and Prime Minister Hwang Kyo-ahn and National Security Adviser Kim Kwan-jin. During the meetings, Mattis is said to have emphasized that "alliance will continue to take defensive measures" in response to North Korean threats.

On his second day in the country, he will hold talks with Defense Minister Han Min-koo. He held a meeting with Foreign Minister Yun Byung-se earlier in the day.

His visit appears to be aimed at reassuring Washington's key allies in Asia that are concerned that the alliance might not be as strong under President Donald Trump, who has accused them of free-riding on U.S. security commitments and asked for more cost sharing.

The US' planned placement of a Terminal High Altitude Area Defense (THAAD) battery in South Korea will also be among key topics to be discussed during his stay here as it has been causing a diplomatic conundrum for Seoul by drawing strong opposition from China. (Yonhap)